versão On-line ISSN 1812-9528

Resumo

Group A streptococci is the most frequent agent of pharyngitis and penicillin continues to be the treatment of choice. Alternative drugs have been developed for allergic patients, such as erythromycin, new macrolides and clindamycin. The level of resistance to macrolides depends on the geographic region and the principal mechanism of resistance is the target modification by methylase enzime. Phenotypically, this resistance pattern is known as MLS resistance. Recently, a new mechanism involving active efflux was described and this pattern has been described with the M phenotype. The aim of this study was to determine the antibiotic resistance of group A Streptococci to erythromycin, azithromycin, clarithromycin, clindamycin and penicillin and to infer the mechanism of resistance. We collected 125 strains of group A Streptococci from pharingoamigdalitis, piodermithis, bacteremias, abscess, otitis. Susceptibility testing was performed by disk difusion method, in Mueller Hinton agar containing 5% sheep blood and incubated at 35°C in a 5% carbon dioxide atmosphere. The mechanism of resistance to erythromycin was evaluated by a double diffusion disk test with erythromycin and clindamycin disks. All strains were susceptible to penicillin, 99.2% were susceptible to clindamycin and there was a 7.2% cross resistance to macrolides. From these isolates, 89% displayed the M phenotype and 11% the MLS phenotype. These results confirm that group A streptococci remains in vitro susceptible to penicillin. The resistance to macrolides was similar to that found in Latin American literature. Respect to erythromycin, the resistance phenotypes found in these isolates belong mostly to M phenotype, mechanism for efflux